Wave guide antenna



QEEENCE HGGFW LAN J. CHU

Jan. 15, 1957 WAVE-GUIDE ANTENNA Filed Jan. 23 1953 United States PatentWAVE GUIDE ANTENNA Lan J. Chu, Lexington, Mass., assignor to The GabrielCompany, Cleveland, Ohio, a corporation of Ohio Application January 23,1953, Serial No. 332,839

22 Claims. (Cl. 343-771) The present invention relates to wave-guideantennas and more particularly to antennas of the type embodying asurface reflector cooperating with a slotted wave-guide structure.

Various techniques have been proposed and utilized for feedingradio-frequency energy to surface reflecting elements, such asparaboloidal reflectors. A wave-guide transmission line, for example,has been mounted through the vertex region of a paraboloidol reflectoralong the axis of the reflector, with the mouth of the guide terminatingnear the reflector focus. A secondary reflector surface positionedbeyond the mouth of the guide redirects the waves propagated along theguide back upon the paraboloidal reflector, whence the waves aredirected as a beam into space. This same structure has, of course, beenused, also, as a device for receiving radio waves from space. In orderto effect this radio-Wave feedingand-directing process efliciently, ithas been proposed to terminate the waveguide mouth, which may be ofrectangular cross section, in a resonant chamber of transversedimensions larger than the smaller wave-guide transverse dimension.Slots are provided in the surface of the resonant chamber facing theparaboloidal reflector parallel to each of the wider sides of the guide,thereby permitting energy to flow from the slots to the portions of thereflector disposed on each side of the guide, or to permit energy topass from each portion of the reflector into the corresponding slot ofthe resonant chamber. Among the disadvantages of such systems, is themechanical complexity of the structure and the difficulty in fabricatingthe same. It is usually customary to taper the wave guide as it joinsthe resonant chamber in order that the slots in the chamber may beplaced close enough together with respect to the wave-length of theradio energy to appear substantially as a point source. It is quitediflicult and costly, however, to provide these tapers in wave-guidestructures, and it is expensive and complicated to manufacture andassemble the associated resonant chambers. A further disadvantage ofsuch systems resides in the relatively narrow band of radio frequenciesthat can be used with tapered guides and resonant chambers.

An object of the present invention is to provide a new and improvedantenna embodying a wave-guide transmission line of this character thatshall not be subject to the above-mentioned disadvantages and that, onthe contrary, is easy and less costly to manufacture, and is adapted forwide-band frequency operation. To achieve these ends, the antenna of thepresent invention comprises, In preferred form, a longitudinallyextending imperforate wave guide within the interior of which radiowaves of predetermined electric-vector polarization may belongitudinally propagated and provided near its mouth with a pair ofslots communicating with the interior of the guide through oppositelydisposed transverse side-wall portions of the guide substantiallyperpendicular to the plane of the said electric vector. A substantiallyplanar conducting surface closes off the mouth of the guide and iceextends outward beyond the said side-wall portions of the guide in aplane substantially parallel to the plane of the said electric vectorand perpendicular to the longitudinal axis of the wave guide. Preferredconstructional details and dimensional limits are hereinafter discussed.

A further object is to provide a new and improved slotted wave-guidestructure.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in the appended claims.

The invention will now be described in connection with the accompanyingdrawings Fig. 1 of which is a fragmentary perspective view of theinvention in preferred form, partly broken away to illustrate details;

Fig. 2 is a section upon a larger scale taken upon the line 2-2 of Fig.1, looking in the direction of the arrows; and

Fig. 3 is a perspective, partly broken away, of a modification.

Referring to Fig. 1, a wave-guide transmission-line section 1 ofrectangular configuration is shown passing through a rectangular hole 2in the vertex region of a paraboloidal reflector 3 and extending alongthe axis of the reflector. The guide 1 is mounted in the vertex region 2by bolting a bracket 4 secured thereto to the outer surface of thereflector 3, shown to the left in Fig. l. An annular conducting plate 5is mounted upon the inner surface of the reflector in the vicinity ofthe vertex region 2 for a purpose that will later be explained. Theguide 1 may be fed with radio energy from, or may feed radio energy to,a further guide section 9, coupled to the guide 1 at the left of thereflector 3, by a conventional wave-guide flange coupling 7. The guidesection 9 may be connected to a receiver or transmitter, not shown. Themouth or right-hand end 6 of the guide 1 is received in a rectangularrecess 17 formed intermediately of a circular planar conducting surfaceor plate 15 disposed preferably at right angles to the guide 1. The baseor end 18 of the recess 17 thus closes oi? the mouth 6 of the guide 1.Transverse planar recesses 21, preferably of rectangular shape, areformed, as by milling, in oppositely disposed side walls of the waveguide 1, illustrated as the upper and lower walls 16 and 22, near themouth or end 6 of the guide. Transverse slots 11 are cut through theupper and lower walls intermediate the milled recesses 21 to cooperatewith the inner space of the guide 1, which may be air or any otherdesired dielectric medium. In order to protect the slots 11 from theatmosphere and to adapt the medium within the wave guide forpressurizing, if desired, windows 19 having substantially the samedimensions as the recesses 21 are secured within the recesses 21,thereby hermetically sealing the slots 11. The thickness of the windows19 preferably corresponds to the depth of the recesses 21 in order thatthe outer faces of the windows 19 may be substantially flush with theadjacent outer surfaces of the wave-guide 1. The windows 19 may be ofany desired radio-wave transparent material, such as polystyrene and thelike, though a preferred window is constituted of Corning Type 707glass.

In practice, a very strong leak-proof joint between the the windows 19of the recesses 21 must be established, suflicient to withstand fromabout 2 /2 to about 12 pounds of pressure of the medium within theguide 1. The following technique has been found particularly well suitedto achieve this end, and to do so consistent with the demands ofmass-production techniques. Once the recesses 21 and the slots 11 havebeen milled or otherwise formed in the upper and lower outer surfaces 16and 22 of the wave-guide 1, the slots 11 are masked as with maskingtape. A heat-curing thermo-setting resin 23, Fig. 2, is then applied tothe unmasked surface of each recess 21. The masks are then removed andthe windows 19 are applied upon the resin 23 in the recesses 21. Astrip, as of teflon, is then placed over each window 19, and a furtherstrip of metal is placed upon each teflon strip, the assembly then beingclamped together and heated to about 120 degrees centigrade. Theassembly is then withdrawn from the heating unit and unclamped. Air orother gaseous bubbles that might be present in the resin layer 23 areforced out by pressing upon the windows 19. The assembly is then againclamped and heat-cured for about an hour and a half at about 180 degreescentigrade. The metal and teflon strips are then removed, leaving thewindows 19 hermetically and securely locked in place within the recesses21. The reason that the teflon strips are interposed, is that teflonwill not adhere to the windows 19 should some of the resin 23 ooze outand over the windows, whereas metal would become stuck to the windows.

The depth of the conducting-surface recess 17 preferably corresponds to,just slightly less than, the distance D from the mouth 6 of the guide 1to the edge of each slot 11 further from the reflector 3, in order thatthe said edge may lie substantially in the plane of the surface of theconducting plate 15, facing the reflector 3. As will later be explained,however, certain variations in the position D of the slot may betolerated. The ends of the milled sections 21 of the guide 1 at themouth 6 may be secured in place in the recess 17 by soft solder, therecess 17 being of somewhat larger dimensions than the transverse guidedimensions in order to permit the securing process to be effected withease and to facilitate removal of the same, if necessary.

The operation of this system as a transmitting antenna appears to besomewhat as follows. Radio waves propagated longitudinally along theguide 1 toward its mouth 6, in, for example, the TE 1 mode, havingvertical electric-vector polarization, represented by E, are radiatedthrough the upper and lower slots 11, the slots lying in planesperpendicular to the electric vector. The energy radiated through theslots 11 becomes initially guided between the upper and lower outersurfaces 16 and 22 of the guide 1 and the adjacent respective upper andlower portions 14 and 20 of the plate 15. From another point of view,the slots 11 may be considered as exciting elements disposedsubstantially along the vertex of a pair of substantiallyright-angularly disposed corner guiding surfaces 14-16 and 2022. Theenergy is thus directed back along the upper and lower outer surfaces ofthe guide 1, reflecting from the upper and lower surface portions 10 and12 of the reflector 3, thereby being directed as a beam into space.Since the separation between the upper and lower guide side-walls 16 and22 of a rectangular guide operated as above described can be made smallcompared to the wavelength of the radio energy, the slots 11. are ratherclose together and for all practical purposes behave substantially as asingle point source, thus taking advantage of the parallel-ray focusingproperties of the paraboloidal reflector 3 to produce thebefore-mentioned directive beam in space. The reverse process takesplace in reception of energy from space.

The optimum position of the slots 11 for producing the most satisfactoryundistorted major radiation lobe in the plane of the electric vector,consistent with maximum antenna gain, has been found to be thatpreviously described, with the distance D substantially the same as thedepth of the recess 17 so that the slot 11 lies just outside the planeof the inner surface of the conducting plate 15. It has been determined,however, that satisfactory, though less desirable, results can beobtained if the slots 11 are disposed somewhat closer to theparaboloidal reflector 3, though intolerable distortion of the radiationlobe pattern and loss of antenna gain has been found to occur if theslots 11 are spaced closer to the reflector 3 than about one-quarter ofthe wavelength of the radio energy from the position D shown .in Fig. 1.It

has also been determined that the transverse dimension L of the upperand lower portions 14 and 20 of the plate 15 should have a value ofabout one-half the said wavelength, though variations therefrom up toabout three quarters of the wavelength may be tolerated. The length ofthe slots 11 is rather critical, though variations in the width of theslots may be effected. The position of the tuning slug 25 at a pointintermediate the slots 11 and the reflector 3, and the depth of the slugpenetration into the interior of the wave guide may be chosen tominimize reflections from the slot radiators 11 for specific lengths andwidths of the slots. It has been found, furthermore, that thisconstruction may compensate for such reflections, providing adequateimpedance matching, over a relatively wide frequency band. Theundesirable effects of that energy which is reflected from the portionsof the reflector 3 back into the slots 11 may also be minimized, butwith the aid of the previously described plate 5 superimposed upon thereflector 3 about the guide 1. While some energy reflected from theouter portions of the re flector 3 may re-enter the slots 11,cancellation or substantial cancellation thereof at the slots 11 hasbeen found to occur as a result of reflections from the surface of plate5 protruding closer to the slots 11 than the adjacent portions of thereflector 3. This effect, moreover, again takes place over a broad bandof frequencies.

Not only does the above-described construction elimimate the necessityfor tapering the wave guide and for providing resonant slotted chambers,but this construction is admirably suited to rapid and accuratemass-production techniques. The broad-band character of the structure,effected through the impedance matching and reflection-compensatingfeatures thereof, moreover, permits its use with many differentradio-frequencies. It has been observed that this structure, inaddition, illuminates or feeds the reflector aperture in such a manneras to provide most satisfactory minimal secondary lobes in the radiationpattern.

As an illustration of typical dimensions, given in units of inchesinstead of fractions of a wavelength, though they may easily beconverted into such, a 7000-megacyclc system may utilize aTEo.1-mode-operated wave guide 1 having side walls about of an inchthick. The recesses 21 may be about /32 of an inch deep and about A. ofan inch wide. The slots 11 may be about of an inch long and of an inchwide and spaced about of an inch from the mouth 6 of the guide 1. Thedepth of the recess 17 in the conducting plate 15 may also be about ofan inch for optimum results. The plate 15 may be of circular contour,about 2% inches in diameter.

While, as before explained, the rectangular guide 1 is particularlywell-suited to the purposes of the present invention inasmuch as theheight dimension, shown vertical, may be small compared to the wavelength of the radio energy, so that the slots 11 may be close together,if some distortion can be tolerated, the same technique may be appliedto wave guides of other configuration, such as guides that are oval incross section. In Fig. 3, as an illustration, a circular guide 1 isshown provided with oppositely disposed arcuate recesses 21, slots 11and windows 19, bounding sectors of a circle. The mouth of the guide 1is closed off by a fiat conducting plate 15. This termination, forpurposes of illustration, is shown as a direct solder connection betweenthe mouth of the guide 1 and the inner face of the plate 15. The sametype of recessed connection at the plate 15 described in connection withFig. 1, could, of course, be used, much as the flat termination of Fig.2 could be used with the rectangular guide of Fig. 1. in the recesses 21of the circular guide 1 of Fig. 2, may be formed almost at the peripheryof the opening at the end of the guide for optimum results, as beforedescribed in connection with Fig. 1.

While the invention has heretofore been described in connection with theuse of suchsystems as transmitting The slots 11 apparatus, it is to beunderstood that they are equally well suited for the reception of radiowaves. The slotted wave guide and end-plate structure, moreover, mayfind application as an antenna in and of itself, without the use of asurface reflector 3, to obtain radiation patterns of the characterproduced by such a slotted guide. If desired, furthermore, but a singleslot may be utilized where symmetrical results are not wanted. Aplurality of unsymmetrically disposed slots may also be employed, ifunsymmetrical patterns are to be achieved, the plurality of slots, forexample, being parallel to one another on one side only of the guide.While the slots 11 have been shown as provided with rounded ends, thisis merely because a milling machine may produce such ends. It is to beunderstood, however, that the slots may be of strictly rectangular orother configuration and that they may be formed by punching and otherprocesses as well. Similarly the plates 15 may be other configurationthan circular. The length and orientation of the slots may also bevaried depending upon the desired radiation pattern configuration. As afurther illustration, the terminal slots may be provided in the narrowerside walls parallel to the Wave-guide axis and perpendicular to the endplate 15.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within the spirit and scope of the inventionas defined in the appended claims.

What is claimed is:

1. A longitudinally extending wave guide closed at one end having a pairof slots in oppositely disposed sides of the guide near the said end anda conducting surface disposed at substantially right angles to the saidsides of the wave guide at the said end and extending transverselybeyond the said sides of the guide.

2. A longitudinally extending wave guide having a pair of slots inopposite sides of the guide disposed a predetermined distance from oneend of the guide and a transversely extending conducting wall providedwith an intermediately disposed recess for receiving and closing otf thesaid one end of the guide, the depth of the recess being less than thesaid predetermined distance, and the conducting wall extendingtransversely beyond the said sides of the guide.

3. A longitudinally extending wave guide, means for transmitting orreceiving radio waves of predetermined electric-vector polarization inthe waveguide, the wave guide being closed at one end and having a pairof slots in oppositely disposed sides of the guide substantiallyperpendicular to the said electric vector near the said end, and aconducting surface disposed substantially at right angles to the saidsides of the wave guide at the said end and extending transverselybeyond the sides of the Wave guide.

4. A longitudinally extending wave guide, means for transmitting orreceiving radio waves of predetermined electric-vector polarization inthe wave guide, the wave guide having a pair of slots in opposite sidesof the guide substantially perpendicular to the said electric vectordisposed a predetermined distance from one end of the guide, and aconducting wall provided with an intermediately disposed recess forreeciving and closing off the said one end of the guide, the depth ofthe recess being less than the said predetermined distance, and theconducting wall extending transversely beyond the said sides of the waveguide.

5. Apparatus as claimed in claim 1 and in which the conducting surfaceextends transversely beyond the said oppositely disposed sides adistance corresponding to from about one-half to about three quarters ofthe wavelength of the radio waves propagated through the wave guide.

6. An antenna comprising a longitudinally extending wave guide withinthe interior of which radio waves of predetermined electric-vectorpolarization may be longitudinally propagated, the wave guide beingprovided near its mouth with a pair of slots communicating with theinterior of the guide through oppositely disposed transverse side-wallportions of the guide, and a substantially planar conducting surfaceclosing off the mouth of the guide and extending outward beyond the saidside-wall portions of the guide in a plane substantially perpendicularto the said side-Wall portions of the guide.

7. An antenna comprising a paraboloidal reflector and a longitudinallyextending wave guide mounted through the vertex of the reflector alongthe axis thereof and within the interior of which radio waves ofpredetermined electric-vector polarization, substantially parallel toone of the wave-guide walls, may be longitudinally propagated, the waveguide being provided near its mouth with a pair of slots disposedsubstantially in the focal plane of the reflector communicating with theinterior of the guide through oppositely disposed transverse side-wallportions of the guide substantially perpendicular to the said onewave-guide wall, and a substantially planar conducting surface closingoff the mouth of the guide and extending outward beyond the saidside-wall portions of the guide in a plane substantially perpendicularto the said one wave-guide wall.

8. An antenna comprising a paraboloidal reflector and a longitudinallyextending wave guide mounted through the vertex of the reflector alongthe axis thereof and within the interior of which radio Waves ofpredetermined electric-vector polarization, substantially parallel toone of the wave-guide Walls, may be longitudinally propagated, the waveguide being provided near its mouth with a pair of slots disposedsubstantially in the focal plane of the reflector communicating with theinterior of the guide through oppositely disposed transverse side-Wallportions of the guide, a substantially planar conducting surface closingoff the mouth of the guide and extending outward beyond the saidside-Wall portions of the guide in a plane substantially perpendicularto the said one Wave-guide wall, and a conducting plate mounted aboutthe wave guide and upon the adjacent regions of the reflector in thevicinity of its vertex.

9. An antenna as claimed in claim 7 and in which the edges of the slotsfurther from the reflector substantially coincide with the planarconducting surface.

10. An antenna as claimed in claim 7 and in which the slots arepositioned a distance corresponding to or less than about one-quarter ofthe wavelength of the said waves from the said planar conducting surfaceand the said surface extends beyond the said side-wall portions of theguide a distance corresponding to from about onehalf to aboutthree-quarters of the said wavelength.

11. An antenna comprising a paraboloidal reflector and a longitudinallyextending wave guide mounted through the vertex of the reflector alongthe axis thereof and Within the interior of which radio Waves ofpredetermined electric-vector polarization may be longitudinallypropagated, the wave guide being provided near its mouth with a pair ofrecesses in the outer surfaces of oppositely disposed transverseside-wall portions of the guide, a slot disposed a predetermineddistance from the said end in each of the said side-wall portions of theguide at each recess, a Window secured within each recess to cover thecorresponding slot, and a substantially planar conducting wall providedwith an intermediately disposed recess for receiving and closing off themouth of the guide and extending outward beyond the said side wallportions of the guide in a plane substantially perpendicular to the saidside-Wall portions of the guide, the depth of the conducting-wall recessbeing less than the said predetermined distance.

12. An antenna comprising a paraboloidal reflector and a longitudinallyextending wave guide mounted through the vertex of the reflector alongthe axis thereof and within the interior of which radio waves ofpredetermined electric-vector polarization, substantially parallel toone of the wave-guide walls, may be longitudinally propagated, the waveguide being provided near its mouth with a pair of recesses in the outersurfaces of oppositely disposed transverse side-wall portions of theguide substantially perpendicular to the said one Wave-guide wall, aslot disposed a predetermined distance from the said end in each of thesaid side-wall portions of the guide at each recess, a window securedwithin each recess to cover the corresponding slot, a substantiallyplanar conducting wall provided with an intermediately disposed recessfor receiving and closing off the mouth of the guide and extendingoutward beyond the said side wall portions of the guide in a planesubstantially perpendicular to the said one wave-guide wall, the depthof the conducting-wall recess being less than the said predetermineddistance, a conducting plate mounted about the Wave guide and upon theadjacent regions of the reflector in the vicinity of its vertex, and amatching device inserted within the waveguide between the reflector andthe said slots.

13. An antenna as claimed in claim 11 and in which the wave guide, theside-wall recesses and windows and the planar conducting-surface recessare substantially rectangular, and the planar conducting surface issubstantially circular.

14. An antenna as claimed in claim 11 and in which the wave guide andthe planar conducting surface are oval and the side-Wall recesses andWindows are arcuate.

15. An antenna as claimed in claim 11 and in which the wave guide andthe planar conducting surface are substantially circular and theside-Wall recesses and Windows bound substantially sectors of a circle.

16. A longitudinally extending wave guide of substantially rectangulartransverse cross-section having an imperforate end wall and theoppositely disposed wider side walls of which are each provided with atransverse slot near the end Wall, the side walls being imperforateexcept for the slots, and a planar conducting surface extendingtransversely beyond the said wider side walls at the said end wall.

17. A longitudinally extending wave guide of substanstially rectangulartransverse cross-section closed at one end and having a transverse slotin each. of the wider sides of the guide near the said end, and aconducting surface disposed at substantially right angles to the waveguide at the said end and extending transversely beyond the said widerside walls to form with each of the portions of the said wider sideWalls near the said end a pair of diverging wave-guiding surfacesexternal to the wave guide.

18. A longitudinally extending wave guide as claimed in claim 1 and inwhich the wave guide is of substantially rectangular cross-section.

19. A longitudinally extending wave guide as claimed in claim 1 and inwhich the wave guide is of oval crosssection.

20. A longitudinally extending wave guide as claimed in claim 1 and inwhich the spacing of the said slots from the said conducting surface issubstantially equal to or less than about one-quarter of the wavelengthof the radio waves propagated Within the wave guide.

21. A longitudinally extending Wave guide as claimed in claim 1 and inwhich the said conducting surface has substantially planar regions andsaid slots are disposed adjacent the plane of the said planar regions.

22. A longitudinally extending wave guide as claimed in claim 1 and inwhich the said slots are disposed with in recesses provided in the outersurfaces of the said oppositely disposed sides of the guide near thesaid end, and the slots are covered by windows secured within the saidrecesses.

References Cited in the file of this patent UNITED STATES PATENTS2,405,242 Southworth Aug. 6, 1946 2,407,068 Fiske et al. Sept. 3, 19462,422,190 Fiske June 17, 1947 2,429,640 Mieher et al. Oct. 28, 19472,479,209 Chu Aug. 16, 1949 2,489,288 Hansen Nov. 29, 1949 2,509,196Cork et al. May 23, 1950 2,520,945 Marindin Sept. 5, 1950 2,539,657Carter Jan. 30, 1951 2,543,468 Riblet Feb. 27, 1951 2,545,472 Kline Mar.20, 1951 2,548,655 Cutler Apr. 10, 1951 2,586,895 Willoughby Feb. 26,1952 2,605,413 Alvarez July 29, 1952 2,605,416 Foster July 29, 19522,624,836 Dicke Jan. 6, 1953 FOREIGN PATENTS 675,245 Great Britain July9, 1952 OTHER REFERENCES Watson: Journal of Institution of ElectricalEngineers, vol. 93, part IIIA, No. 4, page 771 relied on.

